Electrical conductivity of synthetic iron-bearing olivine

The electrical conduction in synthetic, dry polycrystalline, iron-bearing olivine (Fo(90)) was investigated as a first-order approach to the electrical conductivity in the upper mantle. This fundamental study is of great importance to better understand the charge-transport mechanisms seen in olivine. Conduction processes in synthetic samples are not influenced by a complex geological history in contrast to conductivity in natural olivine. The experiments show that the apparent activation energy for conductivity for Fo(90) is 230 kJ mol(-1). In currently accepted defect modeling, natural and synthetic olivine requires a mechanism involving small polaron formation (Fe-center dot (Mg) and magnesium vacancies (V (Mg)) as the dominant diffusing species to explain a fO (2) (1/6) relation to electrical conduction. Here, Fo(90) shows no contribution of small polarons to conductivity at temperatures between 1,000 and 1,200A degrees C and almost no dependence on fO(2). Instead, under reducing conditions magnesium vacancies (and electrons) appear to be the major charge carriers.